1. Field of the Invention
The present invention relates to a method for seaming packed cans and which is applicable with a can seamer for seaming cans of aluminum, iron and the like packed or filled with beer, coffee, juice or the like.
2. Description of the Prior Art
An automatic can seamer for packed cans in the prior art is disclosed in Laid-Open Japanese Utility Model Specification No. 60-171640 (1985). Explaining the operation of such device with reference to FIG. 3, a can body 4 is placed on a lifter 3 having the same rotary axis 12 as a chuck 2 that is driven by a drive mechanism. After a lid 5 is placed on the can body 4 the lifter 3 is pushed up so that the lid 5 and the can body 4 are clamped between the chuck 2 and the lifter 3 and subjected to a compressing force. The lid 5, the can body 4 and the lifter 3 are integrally rotated by driving the chuck 2. Thereafter, a groove 6 of a roll 1 is pressed against an edge portion 5a of the lid 5 (FIG. 4) to deform downwardly and inwardly and then upwardly the edge portion 5a, as shown in FIG. 5. Thereby a flange edge 4a of the can body 4 also is deformed downwardly along with the aforementioned deformation of the lid edge portion 5a. Eventually seaming was effected to completion in such manner that a perfectly folded mouth edge defined by flange edge 4a of the can body 4 was pinched between the edge portion 5a and a seamed lid peripheral portion 5b, as shown in FIG. 6, and thereby attachment of the lid to the can body was achieved. In this prior art method, a rotary axis 11 of the roll 1 and the rotary axis 12 of the chuck 2 are parallel to each other, and the roll 1 moves from the outside in a direction perpendicular to the rotary axis 12 so that it will successively press the edge portion 5a of the lid 5.
In the above-described prior art device, a successive working process is employed, in which the roll 1 is brought close to the edge portion 5a of the lid 5 from the outside in the direction perpendicular to the roll rotary axis 11 and the chuck rotary axis 12 to press the edge portion 5a, and the edge portion 5a is deformed downwardly and inwardly and then upwardly. The larger is the overlap dimension h of the can (FIG. 6), the better is the sealing property between the can and the lid and the better is the appearance of the can. However, in order to enlarge this overlap dimension h, it is required that, when the lid 5 is placed on the can body 4 and when they are compressed by the lifter while clamped between the chuck 2 and the lifter 3, the seaming portion of the lid 5 on the side of the can body 4 should bend exactly at a base portion 7 thereof where the lid 5 and the can body 4 come into contact with each other, to ensure a sufficient "body hook" (fold length) dimension l.
However, in the above-mentioned prior art seaming device, since the structure of the roll 1 is such that it moved from the outside in a direction perpendicular to the rotary axis 12 of the can to press the edge portion 5a, in order to exactly bend the edge portion 5a at the precise location of base portion 7 thereof, a substantially large lifter load and compressing force acting between the lifter 3 and the chuck 2 is necessitated. Accordingly, unless a large lifter load is applied, it is difficult to ensure proper sealing by providing a large overlap dimension h of the seaming portion between the edge portion 5a of the lid 5 and the flange edge 4a of the can body 4. Therefore, in such prior art arrangement, in the case of aluminum cans it is necessary to provide a compressing force or lifter load of about 80 kg. Also, a can wall thickness of 0.12 mm or more is necessary in order to ensure that buckling of the can will not be caused by such high lifter load. Accordingly, the arrangement and structure of the roll 1 in the above-described known device involves the problem that it is impossible to contemplate a reduction of the cost of the can material by reducing the can wall thickness below the above-mentioned thickness of 0.12 mm. Moreover, sometimes fine creases will be produced along the periphery of the seam, and thus there also is the problem that such creases would project into the can body, resulting in deterioration of the sealing property.